Tech Bulletin: Troubleshooting Symphony I/O – No Power On
This Tech Bulletin shows you how to resolve issues when Symphony I/O doesn’t appear to power on.
Reported symptoms include:
- When the AC cable is connected to Symphony I/O, the front panel “A” logo doesn’t light up.
- When the AC cable is connected to Symphony I/O, the front panel “A” logo lights up, but pressing the power switch doesn’t power on the unit. Also, the front panel OLED may be blank or display Firmware Update Mode.
Resolving Power On Issues
Power on issues can usually be resolved by checking for these four conditions:
- Unfinished firmware update
- Improperly seated cables
- Faulty power supply
- Shorted circuit board
Use the Front Panel “A” to Troubleshoot
When the Symphony I/O is working properly, the front panel “A” logo will light as soon as AC is connected to the rear panel AC inlet – it’s not necessary to power on the unit. If AC is connected and the “A” logo doesn’t light, this provides important clues for troubleshooting, described below.
Unfinished Firmware Update
If, during a firmware update, Symphony I/O loses power or the USB connection is interrupted, the unit will power on directly in firmware update mode. In this case, the “A” logo lights and Firmware Update Mode may be displayed on the front panel OLED, or the OLED may be blank.
This issue may be simply resolved by connecting Symphony I/O to the Mac and using the firmware updater to re-load the firmware. Please see Updating Symphony I/O Software, included in the Symphony I/O Release 4.2 download.
Improperly Seated Cables
If, after connecting AC, the “A” logo doesn’t light, its possible that internal cables have become unseated. To resolve this issue, disconnect the AC cable if connected, remove the top cover and verify that the cables shown below are firmly seated in their mating connector.
- AC back panel inlet to power supply
- 2 cables from power supply to Main board
- Main board to front panel display board
While checking the internal cables, check the 64-pin ribbon cable between the Main board and the I/O Module(s) as described in the document “Tech Bulletin – Symphony I/O Ribbon Cables”.
Once cables are re-seated, re-connect the AC cable and verify that the front panel “A” logo lights up. If it doesn’t, proceed to the next step.
Faulty Power Supply
If, after re-seating cables, the “A” logo still doesn’t light, then either the power supply is faulty or another circuit board is shorted, causing the power supply’s output to be pulled down. The quickest way to determine the faulty part requires a simple voltmeter:
- Set the voltmeter to read DC volts; select a range that includes +24 volts.
- Disconnect the AC cable, then disconnect the 8-pin connector between the power supply and the Main board shown below
- Re-connect the AC cable and CAREFULLY measure for +24 volts DC between any red cable and any black cable on the power supply side of the 8-pin cable.
- If 24 volts isn’t present, then the power supply is faulty and must be replaced.
- If 24 volts is present, then proceed to the next step.
Shorted Circuit Boards
If the power supply measures +24 volts while disconnected, it is most likely operating properly. Now, test the power supply when loaded by all internal circuit boards.
- Disconnect the AC cable, re-connect the 8-pin cable to the Main board and re-connect the AC cable.
- Check the “A” logo. If it doesn’t come on with the circuit boards connected, then one of the circuit boards has shorted.
Follow these steps to determine which circuit board has shorted:
- Disconnect the AC cable, disconnect the 64-pin ribbon cable(s) between the IO Module(s) and the Main board (shown below), re-connect the AC cable.
- Check the “A” logo. If it lights when the IO Module is disconnected, then the IO Module is shorted and must be replaced. If 2 IO Modules are installed, connect each one at a time to determine the faulty module.
- If after disconnecting the IO Modules the “A” logo still doesn’t light, disconnect the AC, disconnect the cable between the front panel and the Main board (shown below), and re-connect the AC.
- Since you’ve just disconnected the front panel, the “A” logo can’t light. In order to confirm if the power supply is functioning, measure for 24 v DC at the red & black wires again.
- If the power supply doesn’t measure 24 volts DC, then the Main board is faulty and should be replaced. Here’s the logic we followed to arrive at this conclusion:
- The power supply worked when disconnected:
- The power supply didn’t work when all the circuit boards were connected
- The power supply still didn’t work when the IO modules and the front panel were disconnected but the Main board was connected.
- Conclusion – the Main board is shorted, thus shorting out the power supply’s +24 volt output.
Troubleshooting without a voltmeter
If you don’t have access to a voltmeter, you can still troubleshoot shorted circuit boards by following these steps:
- Connect AC.
- If the “A” logo doesn’t light up, proceed to step 2.
- If the “A” logo doesn’t light up, proceed to step 3.
- If the “A” logo does light up, then the IO Module is shorted and must be replaced.
- If 2 IO Modules are installed, connect them one at a time to determine the faulty module.
- If the “A” logo doesn’t light up, proceed to step 4.
- If the “A” logo does light up, then the initial power supply is faulty and must be replaced.
- If the “A” logo does light up, then the Main is shorted and must be replaced. There are no further parts to test!
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